This invention generally relates to a fan case for turbine engines, and more particularly to a fan case liner including an acoustically active joint.
Conventional turbine and turbofan engines for aircraft include a plurality of turbine blades that rotate within a fan case. The fan case serves as a protective covering to protect the turbine blades and the aircraft. Further the fan case channels airflow into the turbine engine. The inner surface of the fan case is constructed to withstand impacts from objects that may come into contact with the fan case. Further, the inner surface of the fan case includes acoustical features to reduce the noise emitted from the engine.
Restrictions on the amount of noise emitted from a turbine engine are becoming stricter. Accordingly, increased efforts are underway to further reduce the noise emitted from an aircraft engine. It is known to provide a fan case liner with a layer of noise attenuation structures and a face layer including a plurality of openings. The face layer is typically a thin sheet of metal or composite material that provides protection to the noise attenuation structure. Noise causing pressure disturbances emanate through the openings within the face layer into the noise attenuation structure where the pressure disturbances dissipate to reduce the total amount of noise.
The fan case liner includes joints between the several pieces of material used to form the inner surface. These joints typically are required to accommodated assembly of the noise attenuation structure and face layer onto the inside wall of the fan case as well as being able to handle loads generated by thermal expansion. The joint includes a seam within both the noise attenuation structure and the face layer. The seam is typically filled to minimize detrimental effects to airflow through the fan case. The filled in seam typically results in an acoustically dead area relative to the rest of the fan case liner. The acoustically dead area reduces the effectiveness of the fan liner such that noise emitted from the engine may exceed desired levels.
Accordingly, it is desirable to develop a joint and seam for a fan case liner that is acoustically active to improve noise attenuation properties of the fan case liner.